The present invention relates to a system and method for analysing a material using infra-red detection. It relates particularly, but not exclusively, to the design and manufacture of an infra-red detector for use in such a system and method.
Infra-red (IR) radiation is the put of the electromagnetic spectrum that lies between visible light and microwave radiation. The absorption of infra-red radiation by a material gives extremely useful information about the molecular structure of that material. If infra-red radiation is directed through a material some wavelengths will be absorbed by the material and some will be transmitted by the material. Analysis of the resulting absorption spectrum can thus reveal details about the molecular groups present in the material, and can therefore be used to identify the material. This technique is known as infra-red spectroscopy.
Most spectrometers for the infra-red wavelength fall into one of two categories: 1) dispersive or 2) Fourier transform. In a dispersive spectrometer, an optical clement causes light at different wavelengths to be refracted at slightly different angles. Hence by measuring the amount of light at each angle, a spectrum can be obtained. In a Fourier transform spectrometer, an interferometer with a time varying optical path difference causes the intensity of light at different wavelengths to oscillate at slightly different frequencies. By recording these oscillations as a function of time and mathematically performing a Fourier transform on the data, a spectrum is obtained.
In general, instruments that are used to perform infra-red spectroscopy on materials utilise the Fourier transform technique (also known as FTIR), and they also employ a so single detector element. The performance of these instruments is extremely good, but generally they are bulky and not portable. Another disadvantage is that samples are collected and brought to the instrument to be analysed, rather than analysing the sample in situ. A further disadvantage of these instruments is that they are extremely expensive.
An example of such an instrument is manufactured by Mettler Toledo in conjunction with ASI Applied Systems. It consists of a bench mounted FTTR instrument connected via an optical conduit to a small probe that can be immersed into a liquid sample. The price of this instrument is, however, in the region of seventy thousand pounds.
An infra-red spectrometer having multiple IR sources is disclosed In U.S. Pat. No. 5.323,066 (R. G. messerschmidt). The spectrometer has a complex arrangement of mirrors, a spatial light modulator which has deformable mirror elements, and a to controller that deforms the mirror elements in order to obtain the spectra. This arrangement of components is very complex and contains many moving parts.
A method and apparatus for real-time inline material monitoring is described in U.S. Pat. No. 5.021,662 (Texas Instruments). The system includes a infra-red source a diffraction grating, and a set of at least six mirrors which are used to reflect and focus infra-red radiation within the device.
An aim of the present invention is to provide improvements in, or relating to, an infra-red detector, and in particular the use of such a detector in a system for analysing a material using infra-red radiation. Another aim of the present invention is to provide a system that has simpler optics than existing systems, and is therefore cheaper to manufacture. It is a further aim of the present invention that the system is portable, and that in situ analysis of a material is possible.
Embodiments of the invention provide methods of fabricating thermal detectors as claimed in the claims hereof.